It is known to insert paper, paper-mylar, or mylar insulators in slots (or channels) in a core of an armature to prevent electrical contact between wire wound in the slots and the core. Typically, a roll of insulation paper is fed between forming rolls to define a core slot insulator shape, is cut to a length corresponding to the axial length of the core, and is inserted into the core. Machines that use this process to insert insulators in each slot of an armature core are commercially available.
After the insulators are inserted into each slot of an armature core, wire is wound into the slots to define coils of wire. When a first strand of wire falls into one of the insulated slots, the wire tends to move the insulator axially in the direction in which the wire is wound.
If the insulator moves in the slot, a portion of the core may be exposed adjacent a wire. The wire may not thereafter be adequately insulated from the core. Further, at the other end of the core, the insulator will protrude from the end of the core and wound wire may split the insulator at the bend lines of the insulator, resulting in the wire travelling through the split and toward an exposed portion of the core. In either case, the wound armature may have to be scrapped or reworked.
In large armatures, washers may be provided on opposite ends of the armature core before wire is wound and after insulators are slid into the core slots. These washers overlap a radially inwardly located portion of each of the slots in the core and prevent axial movement of the insulators in the core slots. A problem with this approach is that the washers used are relatively expensive and use of washers requires additional manufacturing operations during assembly of an armature.